1. Field of the Invention
This invention relates to tire cord adhesive compositions, and more particularly, to a tire cord adhesive composition for coating polyamide fibers.
2. Description of the Prior Art
It has long been recognized that polyester and polyamide fibers make an ideal reinforcement for automobile tires, rubber timing belts, and other elastomeric products.
Among these polyester and polyamide fibers are rayon, nylon and the like, and more recently, Kevlar, which is a polyaramide fiber sold by the du Pont de Nemours Company, has been found to be useful as a reinforcing fiber. These fibers have the requisite tensile and elongation properties which make them ideal for embedding in an elastomeric matrix for producing reinforced elastomeric materials.
The reinforcing effectiveness of a particular fiber is dependent not only upon the physical properties of the fiber but the degree to which the surface of the fiber adheres to the elastomeric matrix. While it is recognized that mechanically bonded fiber to elastomer has some effectiveness in providing an adequate reinforced product, far superior results are achieved by establishing a chemical bond between the fiber and the elastomeric matrix.
The organic fibers, such as the polyester, polyamide and polyaramide fibers, have new functional groups on the surface thereof which are both capable and available for reaction with the eastomeric matrix during the vulcanization process. Therefore, it has been the practice in the tire building industry to coat the fibers with a size, and more preferably a coating composition, which is reactive with both the surface of the fiber and the elastomeric matrix to form an adhesive bridge chemically binding the fiber to the elastomeric matrix. The adhesive composition, by forming this chemical bond, provides a reinforced elastomeric article with a high degree of strength which takes the full benefit of the physical properties of the fiber and imparts them to the final article.
In the particular case of the polyaramide fiber, i.e. Kevlar, it has been found that the triglycidyl ether of glycerol has been useful in providing adhesion between the fiber and the elastomeric matrix. It is theorized that the high epoxide functionality of this material yields reactive sites which readily interact with both the fiber and the elastomer. In addition, the triglycidyl ether of glycerol has the advantage of having a certain degree of water solubility so that when dissolved and/or dispersed in water it will readily wet the surface of highly polar polyamide of polyaramide fiber.
While the triglycidyl ether of glycerol has been found to be useful as a tire cord adhesive composition, i.e. a fiber coating composition, it is both expensive and difficult to manufacture. Thus, those skilled in the art have attempted to find an economic substitute for the triglycidyl ether of glycerol which is easily produced from relatively inexpensive raw materials while enhancing the performance of the composition and providing superior reinforced elastomeric articles.
In accordance with the present invention, a tire cord adhesive is provided which is economical to manufacture, which is easily produced and which imparts the requisite adhesion between the reinforcing fiber and the elastomeric matrix.
Further, in accordance with the present invention, a tire cord adhesive composition is provided which has the requisite degree of water solubility for ease of application to the reinforcing fiber.